Physical essence of propagable fractional-strength optical vortices in free space

TL;DR

This paper reveals the physical principles behind the stable propagation of fractional-strength optical vortices in free space, focusing on diffraction limits, phase evolution, and phase binary properties to deepen understanding of light behavior.

Contribution

It introduces new physical insights into fractional-strength optical vortices, explaining their stability and phase characteristics in free space, which were previously not well understood.

Findings

Polarization modes are intertwined due to Abbe diffraction limit.

Phase evolution causes polarization rotation in fractional-order vortex beams.

Phase exhibits a binary time vector property, not just scalar.

Abstract

Fractional-order vector vortex beams are recently demonstrated to be new carriers of fractional-strength optical vortices. However, why can those new vortex beams formed by the combination of both unstable states propagate stably in free space? Here, we solve this scientific problem by revealing the physical essence of propagable fractional-strength optical vortices in free space.Three new understandings regarding those peculiar vortex beams are therefore proposed, namely Abbe diffraction limit, phase evolution of vortex beam, and phase binary time vector property.For the first one, owing to Abbe diffraction limit, the inherent polarization modes are intertwined together, thereby maintaining the entire peculiar vortex beams in free space. For the second one, we demonstrate the phase evolution of vortex beam, which is the physical reason of polarization rotation of fractional-order VVBs. For the third one, the phase is not merely a scalar attribute of light beam, but manifests a binary time vector property. This work provides entirely different physical viewpoints on the phase of vortex beam and Abbe diffraction limit, which may deepen our knowledge on the behavior of light beam in classical optics.